The present invention relates to an inspection method for a semiconductor device and, more particularly, to a method of detecting the presence/absence of a void in a contact hole or through hole.
As the semiconductor integrated circuits become more and more micropatterned, the step coverage of a metal interconnection, and particularly an Al metal interconnection, in a contact hole or through hole degrades, and poses problems of conduction failures and increases in interconnection resistance. For this reason, a method of burying an Al alloy material in the contact hole or through hole of a substrate by sputtering has become put into practice. The method of burying the alloy material by sputtering includes a high-temperature sputtering method. According to this method, a semiconductor substrate is heated to several hundred .degree. C. (usually 400.degree. C. or more), and an Al alloy material film is formed by sputtering. The Al alloy material is buried in a contact hole or through hole, while it is set in a reflow state or in a state exhibiting characteristics close to it, to form a film.
With the high-temperature sputtering method, a burying defect is caused by several factors, e.g., when a chamber atmosphere leakage occurs during sputtering or the heating temperature of the semiconductor substrate is low due to the apparatus failure.
In such a case, the burying defect must be detected. When a buried film is formed by the high-temperature sputtering, two types of defects occur, i.e., a defect in which an Al alloy material 5 is not planarized above the upper portion of a contact hole 4, as shown in FIG. 4A, and a defect in which an Al alloy material 5 forms a void 7 in a contact hole 4, as shown in FIG. 4B. Reference numeral 1 denotes a silicon substrate, and 3, an interlevel insulating film.
The burying defect of the type shown in FIG. 4A can be determined by outer-appearance inspection. The burying defect of the type shown in FIG. 4B is conventionally detected by cleaving the contact hole portion and observing the cleaved portion with an SEM (Scanning Electron Microscope). With this method, an accurate evaluation cannot be performed unless observation is performed for a large number of samples, and much time and labor are accordingly required. For this reason, as methods other than those employing cleavage confirmation, the following inspection methods have been proposed.
Japanese Patent Laid-Open No. 6-69307 discloses a method as shown in FIG. 5A. According to this method, the presence/absence of a reacted alloy layer 10 is confirmed. The reacted alloy layer 10 is formed by reaction between an underlying metal 9, e.g., a Ti layer, formed by sputtering in order to improve the burying properties, and an Al alloy material buried in a contact hole 4 by high-temperature sputtering. A burying defect is inspected in accordance with the presence/absence of the reacted alloy layer 10. The presence/absence of the reacted alloy layer 10 is confirmed by removing the Al alloy material on the reacted alloy layer 10 by etching.
Japanese Patent Laid-Open No. 7-297277 discloses a method as shown in FIG. 5B. According to this method, an Al alloy material 5 is buried. The Al alloy material 5 above a contact hole 4 is then removed by etching. A void 7 in the contact hole 4 is inspected with an SEM or the like.
In each prior art described above, the Al alloy material 5 above the contact hole 4 or through hole must be removed by etching, thus increasing the number of steps. This is because the conditions for removing the Al alloy material 5 above the contact hole 4 or through hole by etching and the etching conditions for interconnection formation of the Al alloy material 5 are different.
If a predetermined underlying metal 9 does not exist, the method of inspecting the burying properties by confirming the presence/absence of the reacted alloy layer 10 formed by reaction between the Al alloy material 5 and the underlying metal 9 cannot be employed, because no reacted alloy layer 10 is formed. Even if a reacted alloy layer 10 is formed, since a burying defect may have occurred, a problem may occur in the inspection precision.
This is due to the following reason. When a chamber atmosphere leakage occurs during high-temperature sputtering or the temperature of the semiconductor substrate 1 is decreased for some reason during sputtering, even if a burying defect occurs, a reacted alloy layer 10 is formed.